Pre-formulated powder feedstock

ABSTRACT

A powder composition adapted for use in suspension thermal spray coating processes. The powder includes agglomerated and/or non-agglomerated particles having at least one dispersing agent deposited thereon. The composition results in a homogeneous, stable suspension when combined with a liquid carrier for use in suspension thermal spray coating processes.

TECHNICAL FIELD

The field of art to which this invention generally pertains issuspension thermal spraying.

BACKGROUND

Suspension plasma spraying (SPS) is a relatively new process that isderived from atmospheric plasma spraying (APS) for depositing coatingson various substrate materials. The feedstock for use in such processestypically consist of fine particles suspended in liquid carriers thatare often hazardous in nature, are highly specialized, and thereforepresent challenges relating to processing, handling, storage andtransportation. As a result, there is a desire to provide thesespecialized feedstocks by alternative production and delivery methodsthat are more efficient and cost effective.

The materials and processes described herein meet the challengesdescribed above, and in addition, provide additional benefits andadvantages not currently recognized in this art.

BRIEF SUMMARY

A powder composition is described adapted for use in suspension thermalspray coating processes. The composition includes primary particleshaving at least one dispersing agent deposited thereon, the compositionresulting in a homogeneous, stable suspension when combined with aliquid carrier for use in suspension thermal spray processes.

Additional embodiments include: the composition described above wherethe primary particles are agglomerated and/or non-agglomerated; thecomposition described above where the primary particles are up to about10 microns in size; the composition described above where the primaryparticles are up to about 2 microns in size; the composition describedabove where the primary particles are up to about 0.1 micron in size;the composition described above where the primary particles are about0.01 to about 0.1 micron in size; the composition described above wherethe primary particles comprise at least one of: oxides of aluminum,zirconium, titanium, chromium, manganese cobalt, yttrium, lanthanum,lanthanum strontium, manganese, manganese cobalt iron, dysprosium;carbides of titanium, tantalum, tungsten, chromium, vanadium, nickel;lanthanum strontium manganite, pure metal and/or alloys based on nickel,cobalt iron, chromium, aluminum, copper; yttrium fluoride, lanthanumstrontium cobalt ferrite, zirconia gadolinia ytterbia yttria, gadoliniumzirconate, lanthanum strontium maganate, lanthanum strontium cobaltferrite; zirconia stabilized with magnesia, calcia, dysprosia, yttria,ceria, ytterbia; ytterbium zirconate, strontium, and mixtures and/orcomposites thereof; the composition described above where the dispersingagent is a polymer salt, an inorganic salt, a non-ionic organiccompound, and/or an acid or base that produces dispersion effect throughpH; the composition described above where the dispersing agent is2-[2-(2-methoxyethoxy) ethoxy] acetic acid; the composition describedabove where the dispersing agent is present in an amount of up to about10% by weight; the composition described above where the dispersingagent is present in an amount of up to about 5% by weight; thecomposition described above where the dispersing agent is present in anamount of about 0.1% to about 1% by weight; the composition describedabove where the powder material additionally contains a binder depositedthereon; the composition described above where the binder is polyvinylalcohol; the composition described above where the binder is present inan amount up to about 0.2% by weight; the composition described abovewhere the binder is present in an amount of about 0.01% to about 0.2% byweight; the composition described above where the liquid carrier is anorganic liquid; the composition described above where the carrier is oneor more of a ketone, alcohol, glycol, and or aliphatic hydrocarbons; thecomposition described above where the carrier is one or more of water,acetone, methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyleneglycol, hexane, and/or octane; and the composition described above inthe form of a paste.

These, and additional embodiments, will be apparent from the followingdescriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a spray dried powder described herein.

FIG. 2 shows examples of total carbon measurement for products producedas described herein.

FIG. 3 shows examples of settling rates for products produced asdescribed herein.

FIG. 4 shows examples of mixing times for agglomerates produced asdescribed herein.

FIG. 5 shows an example of a suspension plasma spray coating asdescribed herein.

FIG. 6 shows examples of settling rates for products produced asdescribed herein.

FIG. 7 shows a depiction of a particle with deposited dispersant asdescribed herein.

FIG. 8 shows a depiction of an agglomerate with deposited dispersant asdescribed herein.

FIG. 9 shows a depiction of an agglomerate with deposited dispersant andbinder as described herein.

DETAILED DESCRIPTION

The particulars shown herein are by way of example and for purposes ofillustrative discussion of the various embodiments of the presentinvention only and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show details of the invention in more detail than isnecessary for a fundamental understanding of the invention, thedescription making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

The present invention will now be described by reference to moredetailed embodiments. This invention may, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The terminology used in thedescription of the invention herein is for describing particularembodiments only and is not intended to be limiting of the invention. Asused in the description of the invention and the appended claims, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Allpublications, patent applications, patents, and other referencesmentioned herein are expressly incorporated by reference in theirentirety.

Unless otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by the present invention. Atthe very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, each numericalparameter should be construed in light of the number of significantdigits and ordinary rounding approaches.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Every numerical range given throughoutthis specification will include every narrower numerical range thatfalls within such broader numerical range, as if such narrower numericalranges were all expressly written herein.

Additional advantages of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. It is to beunderstood that both the foregoing general description and the followingdetailed description are exemplary and explanatory only and are notrestrictive of the invention, as claimed.

In the past, SPS feedstock materials have been provided in the form ofready-to-use liquid suspensions, or their individual components ofpowders (consisting of primary particles in agglomerated and/ornon-agglomerated form), liquid media and dispersants as ingredients thatare obtained from separate sources. Primary particles are referred tohere as the smaller discrete particles that appear as single units orform into larger connected structures named here as agglomerates. Apowder is a collection of particles that is composed of primaryparticles and/or agglomerations of primary particles and may includeadditional components such as binders.

Ready-to-use liquid suspensions have inherent disadvantages of complexpackaging, costly transportation and limited shelf life. Whensuspensions are prepared from separate components, the user must haveknowledge of, and account for the correct dosage level of dispersant asa distinct and necessary ingredient of the suspension formulation. Theuser would then calculate, measure, and dispense the prescribed quantityof dispersant according to the required suspension composition.

The ratio or percentage of feedstock powder to liquid media is referredto as the solids loading of the suspension. Suspension compositions mayvary in terms of solids loading depending on the plasma spray equipmentused or other considerations. Solids loading typically ranges from about5% by weight to about 30% by weight, or greater, e.g., up to 50% byweight.

The dispersant being accounted for and controlled by the end user isundesirable from the standpoint of both the manufacturer and the enduser. The manufacturer of a feedstock material that is designed forsuspensions may have knowledge considered to be proprietary in thenature and application of certain dispersants Also, the end user, may beinconvenienced by performing associated tasks of accounting for andhandling dispersants as separate components in making suspensions. Thesystem described herein provides dry feedstock powder containing theoptimum amount of dispersant (i.e. pre-formulated) which eliminatesinvolvement by the end user, and is inducible to proprietary suspensioncompositions. Preferably the dry powder containing the dispersant isfree-flowing, typically non-dusting, and capable of being poured inpowder form, i.e., not a paste or a liquid. The invention provides theoptimum amount of dispersant for the suspension independently and isthus self-correcting for any solids loading chosen by the end user, afeature that does not currently exist. That being said, it is alsopossible to mix sufficient liquid with the dry powder to form a paste,and still realize the benefits described herein, i.e., by the end useradding additional liquid on-site.

A pre-formulated submicron feedstock powder is described herein for usein suspension spray. Current feedstock powders require dispersing agentsto be added as separate components when producing suspensions. Powdersand especially submicron powders that can be loosely agglomerated andpre-loaded with dispersing agents via a spray-drying process provide aready-formulated single component dry feedstock that reduces dusting,improves handling and allows for formulations to be made and qualitycontrolled by the manufacturer. Any dispersing agent typically used insuspension thermal spraying can be used in the processes describedherein, such as, for example, polymer salts, inorganic salts, andnon-ionic organic compounds, etc. While the dispersing agent doesprovide benefits in the spray drying process, the amount and type ofdispersing agent needed for the processes described herein must be suchthat they can produce a homogeneous, stable suspension for thermal spraycoating when combined with the appropriate carrier. Typically suchamounts when deposited on the final powder, represent up to about 10% byweight, with up to 5% by weight of the powder and amounts between about0.1% and about 5% by weight particularly useful. While useful asdescribed in the spray drying process, care should be taken to controlthe amount of dispersant used specifically for use in the suspensionthermal process intended, for example, the use of too much dispersant inthe spray drying process could produce the opposite effect of adestabilization or flocculation, or otherwise inhibit suspension in thesuspension thermal spray process.

While some spray dried submicron powders are commercially available,among other things, they are not pre-loaded with dispersing agents asdescribed herein for use in suspensions in thermal spray. Pre-loading ofdispersant, together with agglomeration of the primary particles,greatly simplifies preparation of suspensions by the end user. Althoughagglomeration of the primary particles is preferred, it is not necessaryin producing the same beneficial effect on the suspension asnon-agglomerated primary particles similarly treated with the samequantity of dispersant by other methods. Dispersants may be depositedonto primary particles or agglomerates of primary particles by variousconventional means. The method of forming a solution consisting of adispersant solute dissolved into a solvent then forming a slurry withparticles, followed by removal of solvent through an evaporation processsuch as drying, leaving the dispersant deposited on the primaryparticles and/or agglomerates formed from the primary particles isgiven. Thus spray drying as one specific example is not a requiredmethod for depositing dispersants onto the particles. Alternativedeposition methods such as involving ordinary oven drying, or directapplication of the dispersant to the particles or agglomerates by dryblending may be employed to similar effect.

Common suspension compositions involve flammable carrier liquids such asethanol and isopropanol, which are often classified as hazardousmaterials. A major problem manufacturers face with the distribution ofsuch fully-made suspensions is that they are difficult and expensive towarehouse and ship, due to the hazardous nature of alcohol, and willform sediments over time. The solutions described herein, among otherthings, allow the end-users to make-up fresh suspensions on-site using afew basic components of a pre-formulated agglomerated powder with, e.g.,user supplied alcohol, and mechanical mixing/dispersing units, thus, forexample, eliminating the need for costly handling, processing, storageand shipment of alcohol that would otherwise be required for fully madesuspensions.

Sub-micron sized primary particles produced by Oerlikon Metco in millsusing water media to a prescribed size distribution (typically about 0.2to about 1 micron) to form a slurry are particularly useful. The milledslurry is transferred to a spray dryer where the water content isadjusted and a dispersant added to a prescribed content prior to drying.Binders can assist in the formation of agglomerates, e.g. sphericalagglomerates, during spray drying and may be used to assist thismanufacturing step provided they do not prevent or inhibit dispersion ofthe submicron particles in the end-use suspension.

The aforementioned milled slurry is subsequently spray dried to producespheres approximately 20 microns to approximately 150 microns in sizethat are composed of loosely agglomerated submicron particles and areloaded with the dispersant. The dispersant is deposited onto theparticles in terms of weight percent. The weight percent used depends onthe nature of the particles (i.e. material composition and surface area)and the liquid media of choice (i.e. whether ethyl alcohol or water orsome other liquid or combinations of liquids are used) and the chemicalnature of the dispersant itself. Exemplary levels of dispersant mayrange from about 0.1% or less up to about 5% or more, for example, up toabout 10% by weight. The dispersant may be deposited onto the particlesby any conventional method, such as spray drying, oven drying or directapplication that may not involve drying.

The resulting product is a powder that preferably has only a smallcontent of free (i.e. non-agglomerated) submicron particles. Theagglomerates formed from the primary particles can be spherical and/ornon-spherical shape, e.g., ranging in sizes up to 10 microns, up to 300microns, up to a millimeter or more, for example, up to 5 millimeters.In fact, as a result of the particular conditions of the spray dryingprocess selected, the agglomerates can range from very small size ofjust several primary particles stuck together, to very large size ofseveral millimeters. As a preferred embodiment, any agglomerate (orprimary particle) size can be used that produces a free flowing,non-dusting powder—that can be poured, and be free flowing—eitheragglomerated or non-agglomerated.

This pre-formulated product may then be packaged, warehoused, sold andshipped as a suspension spray feedstock. The end user would blend thisfeedstock together with water and/or any typical liquid media (e.g.,organic liquid) for suspensions used in suspension plasma sprayincluding, for example, one or more of a ketone, alcohol, glycol, and oraliphatic hydrocarbons, such as, for example, acetone, methyl alcohol,ethyl alcohol, isopropyl alcohol, ethylene glycol, alkanes such ashexane or octane and mixtures thereof, in prescribed proportions (i.e.,about 25% as an example) typically using a dispersing mixer.Conventional dispersion mixing of some form is typically used and mayinclude, but not limited to, commercially available high speed batch orin-line mixers, commercial ultrasonic dispersion systems or jar milling,for example, to make-up the suspension that is subsequently used by asuspension feed system. This approach will enable the end user toprepare fresh suspensions as they need them, and eliminate the costlyand difficult aspects of handling, processing storing and shipping largequantities of alcohol, by the manufacturer, for example.

While any coating material typically used in thermal spray coatingprocesses can be adapted as the feedstock material for the processesdescribed herein, some representative coating materials which can beused with the processes described herein, include, but are not limitedto, at least one of: oxides of aluminum, zirconium, titanium, chromium,manganese cobalt, yttrium, lanthanum, lanthanum strontium, manganese,manganese cobalt iron, dysprosium; carbides of titanium, tantalum,tungsten, chromium, vanadium, nickel; lanthanum strontium manganite,pure metal and/or alloys based on nickel, cobalt iron, chromium,aluminum, copper; yttrium fluoride, lanthanum strontium cobalt ferrite,zirconia gadolinia ytterbia yttria, gadolinium zirconate, lanthanumstrontium maganate, lanthanum strontium cobalt ferrite; zirconiastabilized with magnesia, calcia, dysprosia, yttria, ceria, ytterbia;ytterbium zirconate, strontium, and mixtures and/or composites thereof.

While the feedstock described herein is particularly useful forsuspension thermal spray coating processes, such as, for example,suspension plasma spray (SPS) processes, suspension HVOF (high velocityoxy-fuel) processes, it may be adapted for use in additional thermalspray processes as well. The size of the primary particles produced bythe processes described herein should be such that the particles areusable with suspension thermal spray systems. Typically, primaryparticles up to about 0.1 micron, up to about 1 micron, up to about 2microns, up to about 3 microns, up to about 4 microns, up to about 5microns, up to about 6 microns, up to about 7 microns, up to about 8microns, up to about 9 microns and/or up to about 10 microns can beused, such that homogeneous, stable suspensions can be formed. Whileprimary particles up to about 2 microns, for example, about 0.1 micronto 1 micron, have been found to be particularly useful, very smallprimary particles, e.g., nanoparticles, and other small particles up toabout 0.1 micron, e.g., 0.01 micron to 0.1 micron, can also be used.

Dispersants include, but are not limited to polymer salts such aspolyacrylic acid, 2-[2-(2-methoxyethoxy) ethoxy] acetic acid andpolyethyleneimine, inorganic salts such as sodium metaphosphate andsodium tetraborate, and non-ionic organic compounds such astriethanolamine and TRITON X-100™, and acid and base compounds thatproduce dispersion effect through pH adjustment such as sodiumbicarbonate and citric acid.

Using the correct quantity of dispersant is based on the amount ofpowder in the suspension. Users will typically want suspensions atdifferent concentrations, i.e., 20% solids, 30% solids, etc. thisrequires the end user to know the correct amount of dispersant to use,calculate how much to use, and accurately measure. As described herein,since the correct amount of dispersant is already on the particles, forexample, to produce a liquid suspension with suitable stability,particle dispersion and low viscosity for required material flowproperties in the SPS feeding system, powder loading in any amount canbe used, and the dispersant is always present in the correct amount,without the end user needing to know how much should be added. The userjust adds as much liquid as they desire for their intended purpose, andthe dispersant will already be present at the correct concentration.

The feedstock described herein is substantially dry, that is, themoisture content, typically less than about 0.05% by weight, iscomparable to conventional feedstock powders used for thermal spray.

While the feedstock described herein may be composed of primaryparticles in agglomerated form, it is not required. While agglomerationdoes not improve or enhance the end-use suspension, some potentialbenefits include improved handling characteristics, reduced dusting,improved transfer and flow for the end user, etc.

Conventional binders, such as PVA or other latex, may optionally beincluded for the spray drying manufacturing step, but are not required.It's desirable to use enough binder to promote or facilitateagglomeration, i.e., fewer free particles. But care should be taken notto use so much that it prevents dissolution of agglomerates to releasethe primary particles when a carrier liquid is added. So the amount ofbinder used will depend on the specific binder selected, but typically,for example with PVA, amounts up to about 0.2% by weight have been foundto work well.

Depending on the nature of the particular materials involved, exemplarylevels of dispersant may be used from about 0.01% to about 10%, however,depending on the considerations recited above.

EXAMPLE 1

A pre-formulated dry feedstock of YSZ (yttria stabilized zirconia) isprepared as follows. YSZ (Metco 204B-XCL) is milled to submicronparticle size, as measured by conventional MICROTRAC S3500 measuringinstrumentation to be D 90 <1.0 micro meter (μm) (i.e. 90% of particlesless than 1 micro-meter in size) using a commercial mill to form awater-based slurry MS1. The slurry MS1 is transferred to a spray dryertank with MEEA (2-[2-(2-methoxyethoxy)ethoxy] acetic acid) dispersantand PVA (polyvinyl alcohol) binder added. The slurry is spray dried toform agglomerates 10 microns to 100 microns in size, producing apre-formulated, dry feedstock containing dispersant, designated as PF1,that is packaged and stored for later use. The dry feedstock is combinedwith ethanol to a 25% by weight solids content in a mixing vessel. Acommercial high-speed dispersion mixer is used to fully break-up thespray dried agglomerates and disperse the submicron particles to formthe suspension. The dispersant that is added at the spray drying stepserves to stabilize the suspension. The dispersed suspension is nowready to use for suspension plasma spray. The suspension can be storedin containers prior to use Immediately prior to use the suspension isremixed by simple mechanical means such as overhead stirrer, paint canshaker or shaking the container by hand, or using other similar means ifit has been stored for more than a few hours.

FIG. 1 shows sprayed dried powder with 1% MEEA and 0.02% PVA. The 0.1%level of PVA also appears to be effective in producing sphericalagglomerates. The 0.02% PVA level produces some spheres, with mostlysmaller irregular shaped agglomerates.

EXAMPLE 2

A pre-formulated dry feedstock of YSZ (yttria stabilized zirconia) isprepared as follows. YSZ (Metco 204B-XCL) is milled to submicronparticle size, as measured by conventional MICROTRAC S3500 measuringinstrumentation to be D 90 <1.0 micro meter (μm) (i.e. 90% of particlesless than 1 micro-meter in size) using a commercial mill to form awater-based slurry MS2. MS2 was subsequently dried in an air circulatingoven and then re-slurried with water and 1% MEEA, and then spray driedto produce a sample designated as SD4. No PVA was used. SD4 was testedto monitor changes in MEEA content and effectiveness in suspensionfollowing direct exposure to harsh conditions. Aliquots of SD4 wereprepared as thin beds in trays and put into an environmental chamber setat 50° C. and 80% relative humidity (RH) for 28 days. The samples weresubsequently measured for changes in MEEA content by combustion analysisto measure total carbon content and chemical strength through suspensionstability tests. FIG. 2 shows that MEEA dispersant content on SD4 asmeasured by combustion analysis did not change significantly after 14and 28 days of exposure. The small decrease may be due to measurementscatter. Also, the measured value of close to 1% indicates that thespray drying process did not decrease MEEA content of the powder.

Degradation in the effectiveness of MEEA dispersant throughdecomposition or oxidation may be detected through suspension stabilitytesting by sedimentation rate. The sedimentation rate is measured byresting the suspension in a glass container and observing the top clearliquid phase over time. The sharp interface between the growing clearliquid layer at the top and the settling suspension containing theparticles at the bottom is the sedimentation line. The sedimentationline gradually lowers over time as the suspension settles leaving theclear carrier liquid at the top. The suspension stability, or theeffectiveness of the dispersant is measured by the rate in which thesedimentation line lowers. Sedimentation lines that remain high for thelongest time indicates the best stability. The effectiveness of thedispersant for SD4 after exposure to 50° C. at 80% RH for 21 days iscompared to SD4 stored under ambient condition (20° C.-30% RH for thesame period in a stability test shown in FIG. 3. Test ethanolsuspensions at 25% solids loading were prepared with the two SD4 samplesfor sedimentation rate analysis. The results show that the harshcondition exposure did not alter the effectiveness of MEEA dispersant onspray dried powder, as indicated by the comparable sedimentation ratesover 168 hours.

Spray dried powder with 1% MEEA and 0.02% PVA was mixed with ethanol at25% solids loading using a conventional high speed dispersion mixer toproduce a test suspension 51. The suspension was sampled following 10minutes and 20 minutes of mixing time, and then analyzed by conventionalMICROTRAC for particle size distribution to determine the effectivenessof high speed mixing in reducing the agglomerates to their constituentparticles.

The MICROTRAC measured results in FIG. 4 indicate that 10 minutedispersion mixing time was insufficient in breaking-up the agglomerates.20 minutes of mixing time provided better agglomerate dissolution thatapproached the M measured results produced by 20 minutes of mixingfollowed by several minutes of sonication to fully break up theagglomerates.

Suspension prepared from the dispersion mixer test 51 was evaluated in asuspension feeder (Metco 5MPE-SF) and sprayed onto a steel substratewith a conventional TRIPLEXPRO™-210 plasma spray gun to confirmsuspension handling and coating structure compared to conventionalsuspensions. No feeding issues were reported. The coating structureproduced shows a columnar structure that is comparable with conventionalsuspensions (FIG. 5) using the same parameters.

EXAMPLE 3

Sample PF1 is mixed with ethyl alcohol at 25% solids loading, and thendispersed through sonication treatment to produce stable suspensionsample S2. Sample S2 is an example of a suspension produced frompre-formulated feedstock. Milled slurry MS2 that had been oven dried andthen mixed with MEEA dispersant at 1% solids loading and ethyl alcoholat 25% solids loading and then dispersed through sonication treatment toproduce a stable suspension sample S3. Sample S3 is an example of asuspension produced as a conventional ready-made method. Milled slurryMS2 that had been oven dried and then mixed with ethyl alcohol at 25%solids loading with no dispersant and then mixed through sonicationtreatment produced suspension sample S4 is an example of a suspensionproduced in absence of dispersant. FIG. 6 compares the sedimentationrates of these suspensions, i.e. from pre-formulated feedstock S2,ready-made method with dispersant S3, and ready-made method withoutdispersant S4. Stable suspensions with comparable sedimentation rateswere observed for pre-formulated and ready-made suspensions S2 and S3.The ready-made suspension without dispersant had poor stability asobserved by rapid sedimentation rate.

A depiction of various embodiments described herein are also shown inFIGS. 7, 8 and 9. FIG. 7, for example shows a depiction of a particle 71with dispersant 72 deposited thereon. FIG. 8 shows a depiction of anagglomerate 81 of individual particles 82 with dispersant 83 depositedthereon. And FIG. 9 shows a depiction of an agglomerate 91 of individualparticles 92 with dispersant 93 and binder 94 deposited thereon.

Thus, the scope of the invention shall include all modifications andvariations that may fall within the scope of the attached claims. Otherembodiments of the invention will be apparent to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A powder composition adapted for use insuspension thermal spray coating processes, comprising primary particleshaving at least one dispersing agent deposited thereon, the compositionresulting in a homogeneous, stable suspension when combined with aliquid carrier for use in suspension thermal spray processes.
 2. Thecomposition of claim 1, wherein the primary particles are agglomeratedand/or non-agglomerated.
 3. The composition of claim 1, wherein theprimary particles are up to about 10 microns in size.
 4. The compositionof claim 1, wherein the primary particles are up to about 2 microns insize.
 5. The composition of claim 1, wherein the primary particles areup to about 0.1 micron in size.
 6. The composition of claim 1, whereinthe primary particles are about 0.1 to about 1 micron in size.
 7. Thecomposition of claim 1, wherein the primary particles comprise at leastone of: oxides of aluminum, zirconium, titanium, chromium, manganesecobalt, yttrium, lanthanum, lanthanum strontium, manganese, manganesecobalt iron, dysprosium; carbides of titanium, tantalum, tungsten,chromium, vanadium, nickel; lanthanum strontium manganite, pure metaland/or alloys based on nickel, cobalt iron, chromium, aluminum, copper;yttrium fluoride, lanthanum strontium cobalt ferrite, zirconia gadoliniaytterbia yttria, gadolinium zirconate, lanthanum strontium maganate,lanthanum strontium cobalt ferrite; zirconia stabilized with magnesia,calcia, dysprosia, yttria, ceria, ytterbia; ytterbium zirconate,strontium, and mixtures and/or composites thereof.
 8. The composition ofclaim 1, wherein the dispersing agent is a polymer salt, an inorganicsalt, a non-ionic organic compound, and/or an acid or base that producesdispersion effect through pH adjustment.
 9. The composition of claim 1,wherein the dispersing agent is 2-[2-(2-methoxyethoxy) ethoxy] aceticacid.
 10. The composition of claim 1, wherein the dispersing agent ispresent in an amount of up to about 10% by weight.
 11. The compositionof claim 1, wherein the dispersing agent is present in an amount of upto about 5% by weight.
 12. The composition of claim 1, wherein thedispersing agent is present in an amount of about 0.1% to about 1% byweight.
 13. The composition of claim 1, wherein the powder compositionadditionally contains a binder deposited thereon.
 14. The composition ofclaim 13, wherein the binder is polyvinyl alcohol.
 15. The compositionof claim 13, wherein the binder is present in an amount up to about 5%by weight.
 16. The composition of claim 13, wherein the binder ispresent in an amount up to about 0.2% by weight.
 17. The composition ofclaim 13, wherein the binder is present in an amount of about 0.01% toabout 0.2% by weight.
 18. The composition of claim 1, wherein the liquidcarrier is an organic liquid
 19. The composition of claim 1, wherein thecarrier is one or more of a ketone, alcohol, glycol, and or aliphatichydrocarbons.
 20. The composition of claim 1, wherein the carrier is oneor more of water, acetone, methyl alcohol, ethyl alcohol, isopropylalcohol, ethylene glycol, hexane, and/or octane.
 21. The composition ofclaim 1, in the form of a paste.